This invention relates generally to monolithic reference current generators and, more specifically, to a very compact self-biasing current generator that can be implemented in a bipolar semiconductor process or in a complementary metal oxide semiconductor (CMOS) process.
In the field of analog integrated circuit (IC) design, it is very common to provide a reference current that is proportional to a reference voltage, the reference current being provided though a current mirror.
FIG. 1 shows a typical prior art circuit for providing a reference current lout at the output of a current mirror. An operational amplifier forces the junction between resistor R1 and the source terminal of device M1 to a reference voltage Vref, thereby generating a current I that is equal to Vref/R1 through components M1, M2, and R1. While this circuit appears simple, it requires the operational amplifier along with its bias circuit. A reference current generator such as this is often used to provide stable current sources to critical analog circuits inside a chip. If the current generator requires another bias circuit elsewhere in the chip for its own biasing, it increases the size, power requirements, and complexity of the entire current reference circuit. The biasing circuit for the operational amplifier of FIG. 1 will most likely be very simple and inaccurate, causing undesirable errors in the offset, offset drift, and other parameters of the operational amplifier.
It would therefore be advantageous to provide a self-biasing reference current generator that is compact and capable of implementation in a bipolar semiconductor process or a CMOS process and that generates a reference current output as well as the bias currents required by the rest of the circuit.